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Overview - Chapter 3
Q20 Reference Manual 31
DSP. The DSP (Digital Signal Processor) chip inside the Q20 is what processes all
signals in the digital domain and creates all of the effects (sometimes with the
assistance of the microprocessor). The DSP chip has a limit to how many
instructions (per sample) it can handle. Some effects take up a large number of
instructions, while others take only a few. Generally, reverbs are big DSP hogs,
while most other effects use relatively small numbers of instructions. When you
route Òpatch cordsÓ between Blocks, each connection requires 1% of DSP power (2%
if the level is not 0.0dB). If you run out of DSP power, the error message ÒDSP IS
FULLÓ briefly appears. If this happens, consider substituting an effect that uses
fewer instructions for one of the more DSP demanding effects you may be using.
Effect Memory. The on-board effect memory is primarily used for delay effects, but
sometimes used by reverb effects (for pre-delay). In total you have 5.4559 seconds
(or 5,455.9 ms), although the maximum delay time any single delay effect may
have is 5 seconds. Once this memory has been allocated, the error message ÒEFFECT
MEMORY IS FULLÓ will briefly appear when you try to apply more delay time to
a delay effect than there is memory available. Note: If you have several delay
Effect Blocks in a Program, they will share the total amount of effect memory that
is available. If the total of all delay times equals that of available effect memory,
you will not be able to increase any of the delay times until you decrease the delay
time of one or more of the delay Blocks.
LFOs. The term LFO comes from the days of early synthesizers, where tremolo and
vibrato effects were created using a Low Frequency Oscillator to modulate another
oscillatorÕs pitch, or the filter or amplifier volume. In effect devices, LFOs are used
to create effects such as flanging, chorus and Lezlie speaker emulation. The Q20
provides 4 LFOs per Program. Most pitch effects use 1 LFO, but some use 2. Also,
some of the larger reverb effects use an LFO for a bigger sound. Example: If you try to
add an effect using an LFO and you have already used all four LFOs in other Effect
Blocks, the error message ÒOUT OF LFOsÓ briefly appears.
Microprocessor Assistance. Like most digital electronic music and audio products,
the Q20 uses a microprocessor to run all basic functions like recalling, editing,
comparing, storing, and renaming Programs, etc. However, some of the effect types
use the microprocessor to assist the DSP chip in creating the effect, and the
microprocessor is capable of assisting in this way for only one effect per Program.
Three Pitch effects use the microprocessor: Phasor, Stereo Lezlie and Ring
Modulator. Only one of these three may be used per Program. Example: If you try to
create a Ring Modulator effect type when either a Phasor or Stereo Lezlie effect is
already in use in the Program, the error message ÒBLOCK COMBINATION NOT
ALLOWEDÓ briefly appears.
In the back of this manual, you will find an index of effect types, listing the
percentage of DSP, Effect memory and number of LFOs required by each. Use this as
a reference when one or more categories of limit handling have been exceeded and
you wish to learn what options exist in reorganizing the Program.